Lee Se-dol, one of the world's top Go players, won just one of the matches against the AlphaGo program, missing out on the $1m prize up for grabs.

Demis Hassabis, founder of DeepMind, said the match had been the "most exciting and stressful" for his team.

Lee Se-dol said he felt "regrettable" about the result of the contest.

In Go, players take turn placing stones on a 19-by-19 grid, competing to take control of the most territory.

The game is considered to be much more challenging for computers than chess.

At a press conference held after the final match, Mr Lee said he did not necessarily think AlphaGo was superior to humans.

But he said he had more studying to do, and admitted the matches had challenged some of his ideas about the game Go.

The AlphaGo system was developed by British computer company DeepMind which was bought by Google in 2014.

It has built up its expertise by studying older games and teasing out patterns of play.

Lee Se-dol did win the fourth match against AlphaGo, after which he said: "I've never been congratulated so much because I've won one game."

(Extracts from BBC)